Types
There are few rules governing the type of rock or sand used in Zen gardens. Any type of rock can be used. For esthetic purposes, however, care should be taken when selecting the size and color. Sand should be fine; it should be about the size of the particles found in children's sandboxes. It should also be in natural colors of black, white or brown. As for the size of the rocks, a variety of different shapes will make it look more natural.
Care
Once the sand is in the base of the garden and the rocks are placed on top of the sand, rake the sand in long, curved strokes to represent water. The design does not have to be finite. Change the swirling pattern and the layout of the rocks whenever they get boring. Make sure to use an odd number of rocks in your garden. Keep the garden clutter free so that the rocks and gravel stand out.
Where to Buy
If the garden is going to be a small one, buy the sand or gravel at a pet or aquarium store. If the garden is going to be big, contact a rock quarries or landscapers to purchase the rock. Also, look for interesting rocks around the park or hiking trails to add to the garden.